We're Going to Cover That In Phase 2

Halloween originated from the Pagan festival Samhain, celebrated among the Celts of Ireland and Great Britain. Irish and Scottish immigrants carried versions of the tradition to North America in the nineteenth century. That is why the pic below (which I carved last night) is called a Jack-O’-Lantern.

It can be traced back to the Irish legend of Stingy Jack, a greedy, gambling, hard drinking old farmer who tricked the devil into climbing a tree, and trapped him by carving a cross into the trunk of the tree. In revenge, the devil placed a curse on Jack which dooms him to forever wander the earth at night. While this bedtime parable was told by Irish parents to their children for centuries, the American tradition of carving pumpkins is known to have preceded the Great Famine period of Irish immigration. The carved pumpkin was associated generally with harvest time in America, and did not become specifically associated with Halloween until the mid to late 19th century.
The Wikipedia entry that I quoted above really made me laugh when it talked about the whole “trick or treat” phenomenon in these terms (emphasis mine): “Although the practice resembles the older traditions of guising in Ireland and Scotland, ritual begging on Halloween does not appear in English-speaking North America until the 20th century, and may have developed independently.” Hysterical!